Lithium secondary battery

ABSTRACT

A lithium secondary battery includes an electrode assembly to which an electrode tap is attached, an electrode tap receptor configured to house a portion of the electrode assembly such that a portion of the electrode tap protrudes to an outside, and a case configured to surround the electrode assembly and seal the electrode assembly together with the electrode tap receptor, wherein the electrode tap receptor includes a gas barrier layer.

CROSS REFERENCE TO RELATED APPLICATIONS AND CLAIM OF PRIORITY

The application claims the benefit of Korean Patent Application No.10-2015-0140742, filed on Oct. 7, 2015, at the Korean IntellectualProperty Office, the disclosures of which are incorporated herein intheir entirety by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a lithium secondary battery.

2. Description of the Related Art

Recently, a lithium secondary battery, which is rechargeable andlightweight and has high energy and output densities, has been widelyused as an energy source for wireless mobile devices. Further, asalternative means to solve problems of air pollution and greenhousegases caused from conventional internal combustion engine vehicles usingfossil fuels such as a gasoline vehicle and a diesel vehicle, anelectric vehicle (EV), a hybrid electric vehicle (HEV), a plug-in hybridelectric vehicle (PHEV), or the like have been proposed. The lithiumsecondary battery has been researched as a power source for thealternative vehicles to the internal combustion engine vehicles.

The lithium secondary battery is classified into a lithium ion batteryusing a liquid electrolyte and a lithium polymer battery using a polymerelectrolyte depending on a type of electrolyte, and is classified intocylindrical, prismatic, and a pouch shapes depending on a shape of anexterior material in which an electrode assembly is accommodated.

Among these, since the pouch type lithium secondary battery has anappearance that is made of a metal layer (foil) and a pouch film formedof multi-layers of a synthetic resin layer coated on upper and lowersurfaces of the metal layer, the weight thereof may be more remarkablyreduced than that of the cylindrical or prismatic lithium secondarybattery using a metallic can, such that the pouch type lithium secondarybattery may be lightweight and may be modified into various shapes.

However, in spite of the above-described advantages, since there is alimitation on a molding depth of the pouch film in a structural aspectthereof, cracks easily occur in the pouch film itself during a moldingprocess for housing large sized battery cells, and the metallic layer isexposed from the cracked portion, which causes a reduction in life-spanof the cells.

In addition, the lithium secondary battery is sealed by molding a casefor housing the electrode assembly in a predetermined shape, and bysealing protruding portions of electrode taps. In this case, anunnecessary space is formed in the sealed portion, and thereby causes areduction in capacity of the battery.

Korean Patent Laid-Open Publication No. 2007-0109080 discloses a pouchtype lithium secondary battery having a rounded corner in which a bottomand a side of an electrode assembly housing part formed at a rearsurface of a pouch are met, however, fails to solve the above-describedproblems.

SUMMARY

Accordingly, it is an aspect of the present invention to provide alithium secondary battery which may achieve a high-capacity withoutlimitation on a battery thickness, and may have a high volumetric energydensity.

In addition, another aspect of the present invention is to provide alithium secondary battery having excellent reliability of sealing.

Further, another aspect of the present invention is to provide a lithiumsecondary battery having excellent resistance to permeability, andlong-term durability.

In order to accomplish the above aspects, according to an aspect of thepresent invention, there is provided a lithium secondary batteryincluding: an electrode assembly to which an electrode tap is attached;an electrode tap receptor configured to house a portion of the electrodeassembly such that a portion of the electrode tap protrudes to anoutside; and a case configured to surround the electrode assembly andseal the electrode assembly together with the electrode tap receptor,wherein the electrode tap receptor includes a gas barrier layer.

In the lithium secondary battery according to an embodiment of thepresent invention, the electrode tap receptor may be formed in aplurality of layers, and the gas barrier layer may be included in aninner layer of the electrode tap receptor.

In the lithium secondary battery according to an embodiment of thepresent invention, the gas barrier layer may be formed on a portionwhich contacts with the electrode assembly.

In the lithium secondary battery according to an embodiment of thepresent invention, the gas barrier layer may include at least oneselected from a group consisting of ethylene-vinyl alcohol copolymer;polyvinylidene chloride; polyvinyl alcohol; nylon; polyamide;polyacrylonitrile, linear low-density polyethylene, ethylene-vinylalcohol copolymer, and ionomer copolymer; a metal film; a coating layermade of at least one selected from a group consisting of silica,alumina, rubber, metal, glass and amorphous carbon; and a film having acoating layer in which layered silicate nano particles are dispersed ina polyvinyl alcohol binder.

In the lithium secondary battery according to an embodiment of thepresent invention, the electrode tap receptor may include apredetermined hole through which the electrode tap protrudes to theoutside, and an insulation film is disposed between the hole and theelectrode tap.

In the lithium secondary battery according to an embodiment of thepresent invention, the electrode tap receptor may further include anelectrolyte storage part.

The lithium secondary battery according to an embodiment of the presentinvention may further include a sub receptor provided on an oppositesurface of the electrode assembly relative to one surface to which theelectrode tap is attached to house a portion the electrode assemblyincluding the opposite surface, wherein the sub receptor may include agas barrier layer.

In the lithium secondary battery according to an embodiment of thepresent invention, the electrode tap may include a first electrode tapand a second electrode tap which are attached to surfaces of theelectrode assembly facing each other, and the electrode tap receptor mayinclude a first electrode tap receptor configured to house a portion ofthe electrode assembly such that a portion of the first electrode tapprotrudes to the outside, and a second electrode tap receptor configuredto house a portion of the electrode assembly such that a portion of thesecond electrode tap protrudes to the outside.

In the lithium secondary battery according to an embodiment of thepresent invention, a portion in which the case and the electrode tapreceptor contact each other may be sealed by an adhesive or thermalfusion bonding.

In the lithium secondary battery according to an embodiment of thepresent invention, the case may be made of at least one selected from agroup consisting of polyethylene, polypropylene, polyethyleneterephthalate and polyethylene naphthalate.

Since the lithium secondary battery according to the present inventionincludes the electrode tap receptors having a specific structure, aformation of sealing parts protruding to an outer surface of thebattery, which are indispensable in the conventional pouch typesecondary battery, may not be required, and thereby volumetric energydensity and stability of the battery may be improved.

In addition, since the lithium secondary battery according to thepresent invention includes the electrode tap receptors having a specificstructure, it is possible to achieve a high-capacity battery having asignificantly increased thickness because molding of a case isunnecessary, and reduce defects in insulation resistance of the batterybecause damaging an insulation layer due to a molding process may beavoided.

Further, since the lithium secondary battery according to the presentinvention includes the gas barrier layer in the electrode tap receptor,inflowing and outflowing of gases into and from the battery may beprevented due to obtaining resistance to permeability, thereby improvinglong-term durability.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and other advantages of thepresent invention will be more clearly understood from the followingdetailed description taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 is a perspective view schematically illustrating a constructionof a lithium secondary battery according to an embodiment of the presentinvention; and

FIGS. 2 and 3 are perspective views schematically illustratingstructures of lithium secondary batteries according to embodiments ofthe present invention.

DETAILED DESCRIPTION

The present invention discloses a lithium secondary battery whichincludes: an electrode assembly to which an electrode tap is attached;an electrode tap receptor configured to house a portion of the electrodeassembly such that a portion of the electrode tap protrudes to anoutside; and a case configured to surround the electrode assembly andseal the electrode assembly together with the electrode tap receptor,wherein the electrode tap receptor includes a gas barrier layer, therebyvolumetric energy density and stability of the battery may be improved,because a formation of sealing part protruding to an outer surface ofthe battery, which are indispensable in the conventional pouch typesecondary battery, is not required, and long-term durability thereof maybe improved by preventing inflowing and outflowing of gases into andfrom the battery.

Hereinafter, exemplary embodiments of the present invention will bedescribed in detail with reference to the accompanying drawings.However, since the drawings attached to the present disclosure are onlygiven for illustrating one of various embodiments of present inventionto easily understand the technical spirit of the present invention withthe detailed descriptions below, it should not be construed as limitingthe present invention.

FIG. 1 is a perspective view schematically illustrating a constructionof a lithium secondary battery according to an embodiment of the presentinvention.

The lithium secondary battery according to the present inventionincludes: an electrode assembly 200 to which an electrode tap 100 isattached; an electrode tap receptor 300 configured to house a portion ofthe electrode assembly 200 such that a portion of the electrode tap 100protrudes to an outside; and a case 400 configured to surround theelectrode assembly 200 and seal the electrode assembly 200 together withthe electrode tap receptor 300, wherein the electrode tap receptor 300includes a gas barrier layer.

Since the lithium secondary battery according an embodiment of thepresent invention may house the electrode assembly without molding of acase, a high-capacity battery may be manufactured without any limitationin a cell thickness, a damage in insulation resistance of the batterymay be reduced because there is no problem of damaging an insulationlayer of the case which may occur during a molding process. In addition,since the lithium secondary battery according to an embodiment of thepresent invention is sealed without sealing parts protruding to an outersurface of the battery, which are indispensable in the conventionalpouch type secondary battery, volumetric energy density and stability ofthe battery may be improved. Further, since the lithium secondarybattery according to an embodiment of the present invention includes thegas barrier layer at a portion on which sealing is performed, long-termdurability thereof may be improved by preventing inflowing andoutflowing of gases into and from the battery.

Electrode Assembly

The electrode assembly 200 according to an embodiment of the presentinvention has a construction applied to a secondary battery, andincludes a cathode plate, an anode plate, a separation film disposedbetween the cathode plate and the anode plate for insulating the same,and the electrode taps 100 which are electrically connected to thecathode plate and the anode plate, respectively. Sides of the electrodeassembly 200 to which the electrode tap 100 is not attached aresurrounded by the case 400, and the electrode taps 100 are housed in theelectrode tap receptors 300 to protrude to an outside as describedbelow.

According to an embodiment of the present invention, the electrode tap100 attached to the electrode assembly 200 includes a first electrodetap 110 which may be a cathode tap electrically connected to the cathodeplate, and a second electrode tap 120 which may be an anode tapelectrically connected to the anode plate. Herein, the first electrodetap 110 and the second electrode tap 120 may be attached to surfaces ofthe electrode assembly 200 facing each other, respectively (see FIG.2(a)), or may be attached to the same surface of the electrode assembly200 as each other (see FIG. 2(b)).

The electrode assembly 200 may have a configuration in which the cathodeplate, the separation film, and the anode plate are sequentiallyarranged and wound in one direction, or a configuration in which aplurality of the cathode plates, the separation films, and the anodeplates are repeatedly laminated, but it is not limited thereto.

The cathode plate and the anode plate are coated with a cathode activematerial and an anode active material, respectively. The cathode activematerial may include any material so long as it is generally used in therelated art without particular limitation thereof. For example, in acase of the lithium secondary battery, the cathode active material maybe a lithium-based active material, for example, may include a layeredcompound such as lithium cobalt oxide (LiCoO₂), lithium nickel oxide(LiNiO₂) or a compound substituted with one or more transition metal;lithium manganese oxide such as LiMnO₃, LiMn₂O₃, LiMnO₂, etc.; lithiumcopper oxide (Li₂CuO₂); vanadium oxide such as LiV₃O₈, LiFe₃O₄, V₂O₅,Cu2V₂O₇, etc.; Ni-site type lithium nickel oxide; lithium manganesecomplex oxide; or the like, but it is not limited thereto.

The anode active material may include any material so long as it isgenerally used in the related art without particular limitation thereof.More particularly, carbon-based materials such as crystalline carbon,amorphous carbon, carbon composite, carbon fiber, etc., lithium metal,alloys of lithium and other elements, silicon, or tin may be used. Theamorphous carbon may include, for example, hard carbon, cokes,mesocarbon microbead (MCMB) calcined at a temperature of 1500° C. orless, mesophase pitch-based carbon fiber (MPCF), or the like. Thecrystalline carbon may include graphite materials, for example, naturalgraphite, graphite cokes, graphite MCMB, graphite MPCF, or the like.Other elements used together with lithium to form an alloy may include,for example, aluminum, zinc, bismuth, cadmium, antimony, silicon, lead,tin, gallium or indium, but it is not limited thereto.

A material of the separation film is not particularly limited so long asit is an insulation material, and a material formed of a porous membranemay be preferably used so that ions can pass between the cathode and theanode. For example, an insulating thin film having high ion permeabilityand mechanical strength may be used. For example, a sheet or non-wovenfabric made of an olefin polymer such as hydrophobic polypropylene withchemical resistance; glass fiber; polyethylene, or the like may be used.When using a solid electrolyte such as a polymer as an electrolyte, thesolid electrolyte may also serve as the separation film. Preferably, theseparation film may be a polyethylene film, a polypropylene film, or amulti-layer film made of a combination of these films; or a polymer filmsuch as polyvinylidene fluoride, polyethylene oxide, polyacrylonitrile,or polyvinylidene fluoride-hexafluoropropylene copolymer, etc.

In addition, the separation film may be a film coated with an inorganiclayer on at least one surface of the above-described polymer film. Typesof an inorganic material included in the inorganic layer are notparticularly limited, but may include, for example, oxides containing atleast one metal selected from aluminum (Al), titanium (Ti), zirconium(Zr), barium (Ba), magnesium (Mg), boron (B), yttrium (Y), zinc (Zn),calcium (Ca), nickel (Ni), silicon (Si), lead (Pb), strontium (Sr), tin(Sn) and cesium (Ce). For example, the oxide may include Al₂O₃, TiO₂,ZrO₂, Y₂O₃, ZnO, CaO, NiO, MgO, SiO₂, SiC, Al(OH)₃, AlO(OH), BaTiO₃,PbTiO₃, PZT, PLZT, PMN-PT, HfO₂, SrTiO₃, SnO₃, CeO₂, or the like, but itis not limited thereto. These oxides may be used alone or in combinationof two or more thereof.

Electrode Tap Receptor

The lithium secondary battery according to an embodiment of the presentinvention includes the electrode tap receptor 300 which houses a portionof the electrode assembly 200 such that a portion of the electrode tap100 protrudes to the outside. The electrode tap receptor 300 and thecase 400 to be described below surround and seal the electrode assembly200 together with each other, such that volumetric energy density of thebattery may be improved.

In addition, due to the electrode tap receptor 300 including the gasbarrier layer, the lithium secondary battery may obtain resistance topermeability, and thereby may achieve long-term durability.

In example embodiments of the present invention, a material of theelectrode tap receptor 300 is not particularly limited, but may includea polymer resin generally used in the related art, and a resin capableof being easily injection molded is preferably used. For example, theelectrode tap receptor 300 may include at least one selected from agroup consisting of polyethylene, polypropylene, polyethyleneterephthalate and polyethylene naphthalate, from an aspect of securingthe molding workability, sealing properties and insulation properties.

A material of the gas barrier layer according to example embodiments thepresent invention is not particularly limited, so long as it can securethe resistance to permeability, but may include, for example, at leastone selected from a group consisting of ethylene-vinyl alcoholcopolymer; polyvinylidene chloride; polyvinyl alcohol; nylon; polyamide;polyacrylonitrile, linear low-density polyethylene, ethylene-vinylalcohol copolymer, and ionomer copolymer; a metal film; a coating layermade of at least one selected from a group consisting of silica,alumina, rubber, metal, glass and amorphous carbon; and a film having acoating layer in which layered silicate nano particles are dispersed ina polyvinyl alcohol binder.

The electrode tap receptor 300 according to an embodiment of the presentinvention may be formed in a plurality of layers, and in this case, thegas barrier layer may be included in an inner layer of the electrode tapreceptor 300. More particularly, the electrode tap receptor 300 may beformed in a structure in which an outer layer 300 a and a gas barrierlayer 300 b are laminated, and the gas barrier layer 300 b may be formedon a portion which contacts with the electrode assembly 200, which ispreferable in terms of securing the resistance to permeability.

Referring to FIG. 1, the electrode tap receptors 300 (310 and 320)according to an embodiment of the present invention may house a portionof the electrode assembly 200 to which the electrode taps 100 areattached, and may include a predetermined holes 311 and 321 so that aportion of the electrode taps 100 protrudes to the outside. In order toimprove the reliability of sealing, an insulation film may be disposedbetween the holes 311 and 321 and the electrode taps 110 and 120. Inthis case, the reliability of sealing as well as insulation propertiesmay be improved.

Referring to FIG. 2 (a), in one embodiment of the present invention,when the first electrode tap 110 and the second electrode tap 120 areattached to surfaces of the electrode assembly 200 facing each other,the electrode tap receptor 300 may include a first electrode tapreceptor 310 configured to house a portion of the electrode assembly 200so that a portion of the first electrode tap 110 protrudes to theoutside, and a second electrode tap receptor 320 configured to house aportion of the electrode assembly 200 so that a portion of the secondelectrode tap 120 protrudes to the outside. Herein, the first electrodetap receptor 310 and the second electrode tap receptor 320 may include afirst hole 311 and a second hole 321 so that a portion of the firstelectrode tap 110 and the second electrode tap 120 protrudes to theoutside, respectively.

Referring to FIG. 2 (b), in another embodiment of the present invention,when the first electrode tap 110 and the second electrode tap 120 areattached to any one surface of the electrode assembly 200, the electrodetap receptor 300 may be disposed on one surface of the electrodeassembly 200 to which the electrode taps 110 and 120 are attached, andmay include two holes so that a portion of the electrode taps 110 and120 protrude to the outside, respectively. In this case, the lithiumsecondary battery may further include a sub receptor 330 which isdisposed on an opposite surface of the electrode assembly 200 which hasno electrode tap formed thereon, and may be formed of the same materialas the electrode tap receptor 300. Thus, the sub receptor 330 may sealthe electrode assembly 200 together with the case 400.

The electrode tap receptor 300 according to an embodiment of the presentinvention may seal the electrode assembly 200 together with the case400. To improve the reliability of sealing, a portion in which theelectrode tap receptor 300 and the case 400 contact each other may besealed through an adhesive, or may be sealed by thermal fusion bonding.

Meanwhile, in the lithium secondary battery, the electrolyte inside thebattery is consumed due to repeated charging and discharging. In thisregard, the electrode tap receptor 300 according to the embodiment ofthe present invention may further include an electrolyte storage part300 c. Accordingly, when the electrolyte in the battery is consumed, theelectrolyte stored in the electrolyte storage part 300 c may be used, sothat life-span properties of cells may be improved. The electrolytestorage part 300 c according to an embodiment of the present inventionmay be formed in a portion in which the electrode tap receptor 300 andthe electrode assembly 200 contact each other. A shape of theelectrolyte storage part 300 c is not particularly limited, but may beformed, for example, in a shape of groove at an inner surface of theelectrode tap receptor 300 (see FIG. 1)

According to another embodiment of the present invention, when theelectrode tap receptor 300 is formed in a plurality of layers includingthe outer layer 300 a and the gas barrier layer 300 b, the gas barrierlayer 300 b may be formed as a portion which contacts the electrodeassembly 200, and the electrolyte storage part 300 c may be formed in apredetermined groove shape in the gas barrier layer 300 b.

Case

The lithium secondary battery according to an embodiment of the presentinvention includes the case 400 which may surround and seal theelectrode assembly 200 together with the electrode tap receptor 300.

In general, the case is molded so as to have a predetermined depth forhousing the electrode assembly, and cracks may occur in the case duringa molding process to cause a limitation on a molding depth of the case.To solve this problem, the case is manufactured by a process ofseparately molding upper and lower cases, then sealing these cases.However, in this case, an unnecessary space protruding to an outside isgenerated in the sealed portion, which causes a reduction in volumetricenergy density of the battery.

Meanwhile, since the lithium secondary battery according to anembodiment of the present invention includes the electrode tap receptor300 having the above-described structure, it is possible to achieve abattery having a significantly increased thickness because the moldingprocess of the case 400 is unnecessary, and reduce a damage ininsulation resistance of the battery because there is no problem such asdestruction of an insulation layer during the molding process of thecase. Further, since the lithium secondary battery according to anembodiment of the present invention is sealed without the sealing partprotruding to an outer surface, volumetric energy density and stabilityof the battery may be improved.

Referring to FIG. 1, the case 400 according to an embodiment of thepresent invention may be formed by one sheet, and may be formed in ashape having a predetermined size so as to surround the electrodeassembly 200. A shape of the case 400 is not particularly limited, butmay be appropriately selected according to the shape of the electrodeassembly 200 housed therein, and may employ a hollow prismatic,cylindrical shape, or the like.

The case 400 may seal the electrode assembly 200 together with theabove-described electrode tap receptor 300. In example embodiments, thecase 400 may house the electrode assembly 200 therein while surroundingthe sides of the electrode assembly 200 to which the electrode tap 100is not attached, and the electrode tap receptors 310 and 320 house theportions of the electrode assembly 200 to which the electrode taps 100are attached, such that the case 400 and the electrode tap receptors 310and 320 may seal the electrode assembly 200.

FIG. 3 include perspective views schematically illustrating a structureof sealing the electrode assembly by the electrode tap receptor 300 andthe case 400 in the lithium secondary battery according to embodimentsof the present invention.

Referring to FIG. 3(a), the case 400 may be firstly formed so as tosurround the sides of the electrode assembly 200 to which the electrodetaps 110 and 120 are not attached, then the electrode tap receptors 310and 320 may be disposed on the case 400 so as to overlap the portions ofthe electrode assembly 200 to which the electrode taps 110 and 120 areattached. In this case, the portions in which the case 400 and theelectrode tap receptors 310 and 320 contact each other may be sealed byusing an adhesive or performing additional thermal fusion bonding inorder to improve reliability of sealing.

Referring to FIG. 3(b), the electrode tap receptors 310 and 320 may befirstly disposed at the portions of the electrode assembly 200 to whichthe electrode taps 110 and 120 are attached, and then the case 400 maybe formed thereon so as to surround the electrode assembly 200. Also inthis case, the portions in which the case 400 and the electrode tapreceptors 310 and 320 contact each other may be sealed by using anadhesive or performing additional thermal fusion bonding in order toimprove reliability of sealing.

Any structure and material generally used in the related art may beemployed for the case 400 according to embodiments of the presentinvention without particular limitation thereof. For example, the case400 may have a structure formed by laminating a thermal fusion bondinglayer, a metal layer, and an outer protective layer.

The outer protective layer according to an embodiment of the presentinvention may prevent a damage or corrosion of the metal layer, and alsoprevent the metal layer from being electrically connected with anexternal object.

The outer protective layer may have a single film structure made of anyone material selected from a group consisting of polyethylene,polypropylene, polycarbonate, polyethylene terephthalate, polyvinylchloride, acrylic polymer, polyacrylonitrile, polyimide, polyamide,cellulose, aramid, nylon, polyester, polyparaphenylene benzobisoxazole,polyallylate, Teflon and glass fiber; or a complex film structure madeof two or more of the above materials.

Among the above materials, polyethylene terephthalate, and nylon arepreferably used, and the nylon layer may be a bi-axially stretched nylonlayer.

When the outer protective layer according to an embodiment of thepresent invention has the complex film structure including two or morelayers, each layer may be coupled with each other through adhesivelayers. In this case, a material of the adhesive layer is notparticularly limited so long as it is used in the related art, and theadhesive layer may preferably have a thickness of 3 μm or less.

The metal layer according to an embodiment of the present invention mayblock invasion of an external moisture, gas, etc. to the electrodeassembly 200, and improve a mechanical strength of an exterior member,as well as prevent chemical substances injected into the exterior memberfrom being discharged to an outside.

A material of the metal layer may include at least one selected from agroup consisting of iron, carbon, chromium, manganese, nickel, andaluminum, etc., and may include, for example, any one selected from agroup consisting of an alloy of iron, carbon, chromium and manganese, analloy of iron, chrome and nickel, and aluminum or an equivalent thereof,but it is not limited thereto.

When the metal layer is made of a material containing iron, themechanical strength thereof may be increased, and when the metal layeris made of a material containing aluminum, flexibility thereof may beenhanced. In this regard, aluminum may be preferably used.

The metal layer may be coupled with other layers forming the exteriormember of the present invention, specifically, the outer protectivelayer, a heating layer or a thermal fusion bonding layer through theadhesive layer. Herein, a material of the adhesive layer is notparticularly limited so long as it is used in the related art.

The thermal fusion bonding layer according to an embodiment of thepresent invention may be melted by heat applied to a peripheral portionof an exterior member film during performing a process of sealing theexterior member film among processes of manufacturing the secondarybattery. Similar to the outer protective layer, the thermal fusionbonding layer may have a single film structure made of any one materialselected from a group consisting of polyethylene, polypropylene,polycarbonate, polyethylene terephthalate, polyvinyl chloride, acrylicpolymer, polyacrylonitrile, polyimide, polyamide, cellulose, aramid,nylon, polyester, polyparaphenylene benzobisoxazole, polyallylate,Teflon and glass fiber; or a complex film structure made of two or moreof the above materials.

Among the above materials, polyethylene is preferably used. Thepolyethylene may be used in a structure in which homo-polypropylene andmodified polypropylene may be laminated.

When the thermal fusion bonding layer according to an embodiment of thepresent invention has the complex film structure including two or morelayers, each layer may be coupled with each other through the adhesivelayer. In this case, a material of the adhesive layer is notparticularly limited so long as it is used in the related art.

The case 400 according to an embodiment of the present invention may beformed by one sheet, and may be formed so as to surround theabove-described electrode assembly 200. In this case, as illustrated inFIG. 1, portions in which both ends of the case 400 overlap each othermay be be sealed. For example, the overlapping portion may be sealed byusing an adhesive, or by performing additional thermal fusion bonding. Aposition of the portions in which both ends of the case 400 overlap eachother is not particularly limited, and as illustrated in FIG. 1, theboth ends of the case 400 may overlap each other and may be sealed at aside portion thereof.

When performing thermal fusion bonding at the overlapping portion, thecase 400 may further include a coating layer made of the same materialas the above-described thermal fusion bonding layer on an upper surfaceof the outer protective layer thereof located at a lower side of theoverlapping portion. In this case, since the thermal fusion bondinglayers may be formed throughout a portion in which the upper and lowercases 400 contact each other, reliability of sealing may be furtherimproved.

A plurality of lithium secondary batteries according to an embodiment ofthe present invention may be coupled with each other to be used as asecondary battery pack. The secondary battery pack may be used as apower source for medium and large size devices such as a power tool; anelectric vehicle (EV) such as a hybrid electric vehicle (HEV), a plug-inhybrid electric vehicle (PHEV), etc.; an electric two-wheel vehicle suchas e-bike, e-scooter, etc.; an electric golf cart; an electric truck; anelectric commercial vehicle; or the like.

Examples and Comparative Examples Preparation Example 1—Preparation ofElectrode Assembly

By notching a cathode plate coated with a lithium nickel cobaltmanganese oxide cathode active material and an anode plate coated with agraphite anode active material in a suitable size, respectively,laminating the same, and disposing a polyolefin separation film coatedwith an inorganic layer containing Al between the cathode plate and theanode plate, a cell was fabricated. Tap parts of the cathode and theanode were welded, respectively. A combination of the weldedcathode/separation film/anode was put into a pouch, followed by sealingthree sides of the pouch except one side into which an electrolyte isinjected. In this case, a portion having the tap was included in thesealing portion. After injecting the electrolyte through the remainingone side, the one side was also sealed, followed by impregnation for 12hours or more. The electrolyte was formed by preparing 1M LiPF₆ solutionwith a mixed solvent of EC/EMC/DEC (25/45/30; volume ratio), and adding1 percent by weight (‘wt. %’) of vinylene carbonate (VC), 0.5 wt. % of1,3-propene sultone (PRS), and 0.5 wt. % of lithium bis(oxalato)borate(LiBOB) thereto, and an electrode assembly was manufactured using theprepared electrolyte.

Example 1

As illustrated in FIG. 1, an electrode tap receptor was prepared byextrusion molding a HDPE resin, and a case was made of PET/Al/PP tomanufacture a lithium secondary battery. The electrode tap receptorincluded a gas barrier layer made of ethylene vinyl alcohol copolymer(EVOH) at a portion which contacts the electrode assembly (preparedaccording to Preparation Example 1).

Comparative Example 1

A lithium secondary battery was manufactured according to the sameprocedures as described in Example 1, except that the electrode tapreceptor did not include the gas barrier layer.

Comparative Example 2

Processes of disposing an electrode assembly in upper and lower cases sothat a portion of the electrode taps attached to the electrode assemblyprotrude to an outside without electrode tap receptor, then sealing anouter surface of upper and lower pouches were executed to manufacture alithium secondary battery.

Test Procedure

(1) Evaluation of Resistance to Permeability

After fully charging the lithium secondary batteries manufacturedaccording to the example and comparative examples, followed bystoring/maintaining the same for 4 weeks at 60° C., a capacity retentionratio compared to full charge, and a rate of increase in internal DCresistance (DC-iR) were measured, and the results are described in Table1 below.

If the resistance to permeability in the battery is decreased, externalair and moisture penetrate into the battery to cause a side reactionwith internal materials thereof, and thereby internal DC resistance(DC-iR) may be increased. Therefore, it can be confirmed that, duringstoring the battery at a high temperature in a fully charged state, asthe internal DC resistance (DC-iR) was increased, the resistance topermeability of the battery was decreased.

(2) Measurement of Energy Density Per Volume

Energy density per volume (Wh/L) was measured for each of the lithiumsecondary batteries manufactured according to the example andcomparative examples, and the results are described in Table 1 below.

TABLE 1 Energy Assessment of resistance to density permeability per SOC100%, 60° C. Week 1 Week 2 Week 3 Week 4 volume Exam- Capacity 98.3%97.2% 96.9% 96.4% 424 Wh/L ple 1 retention ratio Rate of 99.5% 102.2%105.6% 108.0% increase in internal DC resistance (DC-iR) (Discharged)Com- Capacity 97.7% 97.1% 96.4% 95.9% 424 Wh/L parative retention Exam-ratio ple 1 Rate of 101.2% 103.2% 109.5% 115.5% increase in internal DCresistance (DC-iR) (Discharged) Com- Capacity 97.9% 97.6% 97.1% 96.8%390 Wh/L parative retention Exam- ratio ple 2 Rate of 99.3% 102.6%104.3% 106.5% increase in internal DC resistance (DC-iR) (Discharged)

Referring to the above Table 1, in a case of Example 1 of the presentinvention, it could be confirmed that the lithium secondary battery hada large volumetric energy density, and showed only 108.0% of a rate ofincrease in internal DC resistance (DC-iR) after 4 weeks because thecase did not include a sealing part protruding to an outside of thebattery, as well as exhibited excellent resistance to permeability dueto the gas barrier layer included in the electrode tap receptor.

However, in Comparative Example 1, it could be confirmed that thelithium secondary battery showed 115.5% of a rate of increase ininternal DC resistance (DC-iR) after 4 weeks, which was significantlyincreased compared to Example 1 because the electrode tap receptor didnot include the gas barrier layer, and in Comparative Example 2 in whichthe lithium secondary battery was manufactured by a process of sealingthe upper and lower pouches, it could be confirmed that the lithiumsecondary battery had significantly decreased volumetric energy densitycompared to Example 1 due to the sealing part included therein.

What is claimed is:
 1. A lithium secondary battery comprising: anelectrode assembly to which an electrode tap is attached; an electrodetap receptor configured to house a portion of the electrode assemblysuch that a portion of the electrode tap protrudes to an outside; and acase configured to surround the electrode assembly and seal theelectrode assembly together with the electrode tap receptor, wherein theelectrode tap receptor includes a gas barrier layer.
 2. The lithiumsecondary battery according to claim 1, wherein the electrode tapreceptor is formed in a plurality of layers, and the gas barrier layeris included in an inner layer of the electrode tap receptor.
 3. Thelithium secondary battery according to claim 1, wherein the gas barrierlayer is formed on a portion which contacts the electrode assembly. 4.The lithium secondary battery according to claim 1, wherein the gasbarrier layer includes at least one selected from a group consisting ofethylene-vinyl alcohol copolymer; polyvinylidene chloride; polyvinylalcohol; nylon; polyamide; polyacrylonitrile, linear low-densitypolyethylene, ethylene-vinyl alcohol copolymer, and ionomer copolymer; ametal film; a coating layer made of at least one selected from a groupconsisting of silica, alumina, rubber, metal, glass and amorphouscarbon; and a film having a coating layer in which layered silicate nanoparticles are dispersed in a polyvinyl alcohol binder.
 5. The lithiumsecondary battery according to claim 1, wherein the electrode tapreceptor includes a hole through which the electrode tap protrudes tothe outside, and an insulation film is disposed between the hole and theelectrode tap.
 6. The lithium secondary battery according to claim 1,wherein the electrode tap receptor further includes an electrolytestorage part.
 7. The lithium secondary battery according to claim 1,further comprising: a sub receptor provided on an opposite surface ofthe electrode assembly relative to one surface to which the electrodetap is attached to house a portion the electrode assembly including theopposite surface, wherein the sub receptor includes a gas barrier layer.8. The lithium secondary battery according to claim 1, wherein theelectrode tap includes a first electrode tap and a second electrode tapwhich are attached to surfaces of the electrode assembly facing eachother, and the electrode tap receptor includes a first electrode tapreceptor configured to house a portion of the electrode assembly suchthat a portion of the first electrode tap protrudes to the outside, anda second electrode tap receptor configured to house a portion of theelectrode assembly such that a portion of the second electrode tapprotrudes to the outside.
 9. The lithium secondary battery according toclaim 1, wherein a portion in which the case and the electrode tapreceptor contact each other is sealed by an adhesive or thermal fusionbonding.
 10. The lithium secondary battery according to claim 1, whereinthe case is formed of at least one selected from a group consisting ofpolyethylene, polypropylene, polyethylene terephthalate and polyethylenenaphthalate.